Exhaust gas purification filter

Details Exhaust gas purification filter Exhaust gas purification filter

2001-12-20

2004-09-14

Lawrence, Frank M. (Department: 1724)

Gas separation

With separating media bypass or system gas pressure relief

C055SDIG003, C428S116000

Reexamination Certificate

active

06790248

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exhaust gas purification filter.
2. Description of the Related Art
As a means for purifying the carbon particulates, or the like, emitted from an internal combustion engine for an automobile, etc., a method has been employed in which the particulates are trapped temporarily by a filter and subsequently burned off by heating or using a catalyst.
The filter coated with a catalyst is so configured that a honeycombed structure having a multiplicity of cells makes up an exhaust gas purification filter of which the partitioning walls are coated with the catalyst. The conventional exhaust gas purification filter, as shown in
FIGS. 10 and 11
, uses a honeycombed structure having cells
90
having alternate ends thereof closed by plugs
95
. Specifically, as shown in
FIG. 11
, the cell end portions in the upstream end surface
91
are alternately closed by the plugs
95
in a checkerwork form, for example. On the downstream end surface
92
, on the other hand, the end portions of the cells
90
having the upstream end portions thereof not closed by the plugs
95
are closed with the plugs
95
, while the end portions of the cells
90
having the upstream end portions thereof closed with the plugs
95
are left open. Under this condition, the catalyst is carried on the partitioning walls
98
.
The use of this exhaust gas purification filter
9
described above makes it possible to trap the particulates on the partitioning walls when the exhaust gas of the internal combustion engine is passed therethrough, which particulates are burnt off, by a catalyst, with the heat of a high-temperature exhaust gas.
The conventional exhaust gas purification filter
9
described above, however, poses the problems described below.
The particulates
88
flowing in the exhaust gas
8
and trapped on the exhaust gas purification filter
9
are not always burnt off at an appropriate time but may be steadily deposited on the partitioning walls
98
, as shown in FIG.
12
. As long as an exhaust gas
8
low in temperature is being emitted from the internal combustion engine, for example, the burning is not started even by the catalytic action but the particulates
88
only continue to be deposited. In such a case, the pressure loss caused when the exhaust gas
8
passes through a filter, i.e. an exhaust gas purification filter
9
is increased while, at the same time, posing the problem that the filter is eventually heated abnormally and cracked or melted by the combustion heat.
SUMMARY OF THE INVENTION
The present invention has been developed in view of the problem points of the prior art described above, and the object thereof is to provide an exhaust gas purification filter capable of suppressing the generation of excessive pressure loss and preventing the melting due to the deposited particulates.
According to a first aspect of the invention, there is provided an exhaust gas purification filter, for trapping the particulates in the exhaust gas, wherein the pressure loss caused when the exhaust gas passes through the exhaust gas purification filter increases until the amount of the particulates deposited in the exhaust gas purification filter reaches a predetermined value, while the pressure loss is not substantially increased after the amount of the particulates deposited exceeds a predetermined value.
In the exhaust gas purification filter according to this invention, as described above, even in the case where the amount of the particulates deposited increases to such an extent that the pressure loss due to the exhaust gas passing through the filter is increased, the pressure loss is not substantially increased after the amount of the particulates deposited reaches a predetermined value. As a result, an excessive pressure loss can be prevented even in the case where the process for burning off the particulates deposited is carried out belatedly and the amount of the particulates deposited exceeds the predetermined value described above. In this way, the adverse effect that the increased pressure loss otherwise might have on the internal combustion engine, etc. can be suppressed.
The exhaust gas purification filter according to this invention may be formed of a honeycombed structure of a metal instead of ceramic.
According to a second aspect of the invention, there is provided an exhaust gas purification filter wherein the predetermined amount of the particulates deposited is preferably smaller than the amount which makes the partitioning wall melt due to the heat generated when burning the deposited particulates. Then, in the case where particulates exceeding a predetermined value are deposited, the trouble of the exhaust gas purification filter being melted can be reduced.
According to a third aspect of the invention, there is provided an exhaust gas purification filter of a honeycombed structure, having a multiplicity of cells surrounded by partitioning walls,
wherein at least some of the cells each have a plug at one of the end portions thereof,
wherein at least some of the plugs to be arranged on the downstream side in the fluid path are partial plugs having an opening allowing the fluid to pass therethrough, and
wherein the pressure loss caused when the fluid entering the cells passes through the partitioning walls is smaller than the pressure loss caused when the fluid passes through the partial plugs.
Now, the operation of this invention will be explained.
The exhaust gas purification filter according to this invention comprises partial plugs each having an opening on the downstream side of the cells. These partial plugs are related to the pressure loss as described above. In other words, the partial plugs are configured to have a larger passage resistance than the partitioning walls against the fluid.
For this reason, the exhaust gas constituting a fluid entering the cells, is not substantially passed through the openings, if any, of the partial plugs but is passed through the partitioning walls and discharged from the adjacent cells having no plugs.
As a result, the particulates in the exhaust gas are trapped by the partitioning walls and appropriately burnt off by the heat of the heater or by the action of the catalyst carried on the partitioning walls of the exhaust gas purification filter.
In the case where the particulates are not readily burnt by the heat of the heater or by the catalytic action, on the other hand, the particulates come to be deposited steadily on the partitioning walls. In such a case, the pressure loss caused when the fluid passes through the partitioning walls increases to a level larger than the pressure loss caused in the partial plugs.
Under this abnormal condition, with the particulates deposited excessively, the fluid that has entered the cells can be discharged from the openings of the partial plugs, and thus the excessive pressure increase under the abnormal condition can be avoided. After the particulates are burnt off by the catalytic action subsequently, therefore, the filter is regenerated into the initial state so that the fluid again begins to flow through the partitioning walls to restart the trapping of the particulates.
With the exhaust gas purification filter according to this aspect of the invention, therefore, an excessive pressure loss caused by the deposited particulates can be suppressed while at the same time making it possible to prevent cracking and fusion loss.
According to a fourth aspect of the invention, there is provided an exhaust gas purification filter of a honeycombed structure, wherein each of the end surfaces of the exhaust gas purification filter preferably includes the cells ends having a plug and the cell ends having no plug alternately arranged. This arrangement can readily establish a route along which the exhaust gas passes through the partitioning walls.
According to a fifth aspect of the invention, there is provided an exhaust gas purification filter of a honeycombed structure, wherein all the plugs located on the upstream side of the ho

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